Measuring characteristics of plastic bottles is well known and standardized test methods for such exist within industry. For example, it is known to measure the wall thickness of a plastic bottle using a system that employs a broadband light source, a chopper wheel, and a spectrometer to measure the wall thickness of the plastic bottle as it passes between the light source and the spectrometer after being formed by a blow molder. The broadband light source in such a system provides chopped IR light energy that impinges the surface of the plastic container, travels through both walls of the container, and is sensed by the spectrometer to determine absorption levels in the plastic at discrete wavelengths. This information is used to determine characteristics of the plastic bottle, such as wall thickness. Other machines are available from several manufacturers throughout the world. Exemplary of such machines is the AGR TopWave Petwall Plus Vision system. This machine performs a thickness measurement of plastic containers by measuring the difference between a PET absorption wavelength and a non-absorption reference wavelength.
In practice, such systems use an incandescent bulb to generate broadband light within the visible and infrared spectrums of interest. The broadband light is chopped, collimated, transmitted through two walls of the plastic container, and finally divided into wavelengths of interest by the spectroscope. This sampling process is limited in both speed and response time.
The state of the art in blow molding technology continues to increase the sampling speed required. This will, in time, render the current technologies used to measure container characteristics unusable.